Script versus novel
Philomena McDonagh's script for this film is truly exceptional. She remains faithful to Christie's story while also managing to include several embellishments that actually improve on the source material - and staying true to the spirit of Christie. Obviously, the distinctive post-war feel has had to go (i.e. because the series is set in 1930s), but only minor changes have had to be made to make that work. The rest of the changes are more important. First, McDonagh adds an opening sequence with Entwisthle and Poirot on the train. He describes the dramatis personae to Poirot, and this inter-cuts with flashbacks to the day of the funeral. This is an effective way of letting the viewers get an overview of this admittedly large ensemble of characters, rather like the family tree in Christie's novel. Second, George becomes Helen's son, and Susan Banks becomes Susannah Henderson. She is no longer married to borderline lunatic Gregory Banks but has instead become a missionary (rather like Lynn in Taken at the Flood). Third, Cora Lansquenet has become Cora Galaccio here, and her French (now Italian) ex-husband takes the role that was given to Alexander Guthrie in the novel, evaluating the paintings. Fourth, McDonagh adds a subplot / red herring in the shape of a missing will (bringing to mind the short story 'The Case of the Missing Will'). George was expected to inherit everything, but he forged a new will to disinherit himself. Fifth, Mr. Goby, Poirot's private investigator, is disposed of, and so is Poirot's rather unbelievable disguise as M. Pontalier. Instead, Poirot is introduced (as himself) much earlier, and he interviews all the family members. Sicth, Miss Gilchrist doesn't start working for Richard and Maude, but is persuaded by Poirot to stay at the house. Seventh, Entwisthle's sister is removed, and he falls in love with Helen Abernethie. Seventh, George and Susannah are revealed to be having an affair in the denouement scene. A somewhat strange addition, but it's done quite nicely in the film. Eight, Rosamund considered abortion but ends up visiting nuns because she feels ashamed. Ninth, the Vermeer painting becomes a Rembrandt (probably because Rembrandt is more well-known to modern audiences). Also, Timothy's ability to walk isn't revealed until the end of the film - he broke into Mr Entwisthle's office to get hold of the deeds to the house. All in all, however, the script is cleverly written, and it's a shame McDonagh never wrote any other Poirot scripts.
Directing, production design, locations, soundtrack
Maurice Phillips's direction is a joy to watch. I particularly like the sweeping camera shots (see the funeral scenes), almost like a bird listening in to the conversations (c.f. the descriptions of Cora). The location used for Enderby is magnificent - Rotherfield Park in Hampshire. Other locations include the Bluebell Railway (Horsted Keynes Station and the Sharpthorne Tunnel), Putney Vale Cemetery and Crematorium, Normansfield Hospital Theatre, The New Wimbledon Theatre, Lincoln's Inn, London (Timothy's house and the convent). Stephen McKeon's soundtrack is suitably dark for the plot, and several tracks can be found on his website.
Characters and actors
Suchet continues to explore Poirot's loneliness ('the journey of life, it can be hard for those of us who travel alone, mademoiselle'). The guest actors do an excellent job portraying their characters, with well-known faces like Michael Fassbender and Geraldine James. But Monica Dolan is the star. What a performance! Breath-taking, completely chilling and emotional at the same time. Quite possibly the best guest act of the entire series.